Field of the Invention
The present invention is related to a control circuit, and more particularly to a control circuit which can be widely utilized to control the slope of output voltage levels of various controller-area-network bus application systems and the like.
Description of the Prior Art
As known, controller area network (CAN) is a kind of specification established in early 1990's, got standardized as ISO 11898-1 in 1993, and widely used in all kinds of vehicles and electronic devices later on. In general, controller area network includes a serial bus, which provides high security level and efficient real-time control. Also, it is able to ensure debugging and priority determining mechanism, thereby making transmissions for internet messages much more reliable and efficient than ever. From this point of view, it is believed that the controller area network nowadays not only has highly flexible adjustment ability which can accommodate more station numbers in existed internet without modifying its software and/or hardware, but also enhances network upgrading conveniences since its data transmission path need not build upon certain specific standard stations.
Please refer to FIG. 1, which is a schematic drawing of a conventional controller area network bus, wherein two stations, i.e. a station 101 and a station 103 are disposed in the controller area network and are individually connected to a common bus 300 through each of the can-transceivers 200. A high-level output CANH and a low-level output CANL are utilized to provide a differential signal so as to achieve transmitting signals. In the digital logic design nowadays, for example as shown in FIG. 2, when the high-level output CANH and the low-level output CANL are both 2.5V, then the digital signal output will be “1”. On the other hand, when the high-level output CANH is raised to 3.5V and the low-level output CANL is lowered to 1.5V, then the digital signal output will become “0”. Speaking of maintaining a dynamic balance of the circuit, an U.S. Pat. No. 7,183,793 has disclosed a certain circuit diagram in which a current source is used for providing biasing voltages in one end of the circuit while operational transconductance amplifiers (OTA) are used for producing loop control currents in the other end when controlling its transistors therein to operate under a saturation region. As such, the electrical currents flowing in two different paths will become equivalent. Meanwhile, by controlling the slopes of amplifying current and reduction current of the current source, the conventional art thereby achieves symmetrical control of its high-level output and low-level output and performs slope control ability of the circuit.
However, it shall be noticed that in order to achieve the slope control ability, a great number of electronic components must be used no matter from the systematic design or IC chip design point of view. In addition, the circuit complexity would be accordingly increased as well. Also, most of the prior arts nowadays can only provide solutions based on different connection methods of the components disposed in the logic circuit. Under such circumstances, to design such a perfect circuit would become a difficult job to do, and the production cost for the circuit and numbers of components must be dramatically raised too, which induces severe budget issues.
On account of all, it should be apparent and obvious that there is indeed an urgent need for the professionals in the field for a novel slope control circuit to be developed so as to solve the above-mentioned problems occurring in the prior design.